Field of the Invention
The present disclosure relates to a focus adjustment device and a control method of the same. More specifically, the present disclosure relates to a technique relating to autofocusing used in electronic still cameras, videos, mobile phones, and the like.
Description of the Related Art
In digital cameras and video cameras, a general autofocusing method uses an output signal from an image sensor such as a charge-coupled device (CCD) sensor and a complementary metal-oxide semiconductor (CMOS) sensor, and detects a signal according to the contrast of a subject to perform focusing. In the above-described method, the contrast of the subject is sequentially detected while moving a focus lens throughout a predetermined moving range in an optical axis direction, and a position where the contrast reaches its peak is determined as a focus position of the focus lens.
With the above-described determination method, however, in a state before the lens is moved, it is difficult to determine in which direction the focus lens is to be driven.
In this manner, the lens drive direction cannot be determined in the state before the lens is moved. This causes a disadvantage in that focus adjustment requires time.
In connection with the drive direction of a focus lens, Japanese Patent Publication No. 61-10044 discloses the configuration of a focus position detection device that can easily determine in which direction the focus lens is to be driven and adjusted, by effectively utilizing chromatic aberration of the lens.
More specifically, the focus position detection device disclosed in Japanese Patent Publication No. 61-10044 detects light beams of two or more types having wavelengths different from each other, from among light beams transmitted through the focus lens, with light reception means arranged at positions optically equivalent to each other with respect to the focus lens. In addition, the focus position detection device is characterized by the configuration of determining a focus adjustment direction of the focus lens based on the difference between outputs from the respective signals that is caused by the chromatic aberration of the focus lens.
In the conventional technique disclosed in Japanese Patent Publication No. 61-10044 mentioned above, however, the configuration of the device needs to include a special detector for determining a focus adjustment direction.
In addition, in FIG. 4 on Page 3 of Japanese Patent Publication No. 61-10044 mentioned above, an intersection point of graphs of a focus evaluated value of blue color and a focus evaluated value of red color is indicated as a focus position. Nevertheless, the intersection point of the graphs of the focus evaluated value of blue color and the focus evaluated value of red color does not actually correspond to a focus position in some cases, because focus positions of red, blue, and red light beams are different from one another depending on the aberration generation statuses. Thus, if the focus is adjusted to a lens position corresponding to the position of the intersection point, a focus adjustment error may increase and a focus adjustment direction may be erroneously detected in the vicinity of the intersection point.